Search

Structural and material symmetries can be engineered to create unique electromagnetic effects including backscattering-immune propagation. In this work we investigate the scattering properties of a class of structures with combined rotational and dual symmetries, i.e., self-dual structures. We demonstrate how self-duality will be manifested through different forms of zero backscattering in periodic and non-periodic structures.

Self-dual structures, ones that remain unchanged under interchanging electric and magnetic portions of the structure where e r = μ r , except for a 90° rotation around their axis, have been shown [1] to produce perfect zero backscattering to an arbitrarily polarized, normally incident plane wave. This phenomenon can be used to create inherently matched radiating apertures made of point-like elements. In [2] , the radiation characteristics of such elements were presented, showing that the element patterns are quite similar to those of an isolated element in free space, being fairly well-behaved and free of blind spots. In this work, we further elaborate on the feeding and matching of these elements in a waveguiding network, with the radiation taking place into a waveguide simulator environment.

Self-dual balanced structures, comprising finite electric and magnetic regions, are invariant to 90 degrees rotation if electric and magnetic regions are interchanged with the rotation. Such structures will produce no backscattering when subject to plane wave illumination along the axis of rotation provided that the Weston balanced condition ∊ r = μ r is obeyed. When higher order spatial harmonics are suppressed, e.g. in a periodic structure whose unit cell is smaller than the wavelength, the entire incident power is forced to be transmitted through the structure. With proper design, this phenomenon can be exploited to produce absorbers over a wide range of frequencies, provided that the constitutive parameters adhere to the Weston condition throughout this range.

The unique matching properties of self-dual structures provide a rich platform to engineer and control the distribution of the power inside such structures. For instance, narrow gaps embedded inside a self-dual structure can be designed to predominantly carry the incident energy into the outbound interface of the structure. This phenomenon can be used to create quasi-matched radiating apertures made of point-like radiating elements. These elements possess patterns that are quite similar to those of an isolated element in free space, being fairly well-behaved and free of blind spots. These characteristics are envisioned to be of great interest for highly demanding applications of phased arrays.

Self-dual structures, whose electric and magnetic parameters can be interchanged without causing any change to the structure, are shown to be inherently matched to free space. With proper design, in such structures, the normally incident energy is funneled through arbitrarily thin air gaps that support TEM or quasi- TEM modes. A finite-length self-dual waveguide, as suggested herein, is inherently matched at both input and output interfaces, even though the field within the waveguide may be substantially complex and have its own characteristic polarization. This structure looks promising for several applications, as detailed below.

The ability to manipulate electromagnetic waves on scales much smaller than the wavelength is of great interest for various applications in device miniaturization, sensing, and nonlinear wave generation. Surface plasmon polaritons provide a natural solution to this problem through localized resonances. Here, we introduce an alternative novel platform to create deeply sub-wavelength hot-spots in periodic arrangements. The localized power is shown to be guided within narrow hollow channels across electro-magnetically thick surfaces composed of complementary low/high impedance electric and magnetic dielectrics. We will discuss physical intuitions on the observed localization phenomenon along with some numerical examples.

In this work the design of an ultrathin carpet cloak based on a metasurface with ring resonators is demonstrated. The scattering from a triangular bump of a Gaussian beam is suppressed by manipulating the reflection phase along the edge of the bump. This is achieved by an array of closed ring resonators with varying radii. The object to hide can be placed under the bump on a flat ground plane. The performance of the designed cloak in the near field and far field is numerically analyzed at the operation frequency and the successful concealing of the bump is confirmed. The presented cloak has a thin, lightweight design and can find applications in radar and antenna systems.

Gradient metasurfaces have recently received significant attention for the unique opportunities they offer for advanced wave manipulation. Such metasurfaces are usually discrete implementations of surface impedance profiles, which are analytically derived to yield the desired operation. Several recent numerical and experimental studies have shown that gradient metasurfaces can work very well over large bandwidths, extending to frequencies where the definition of surface impedance is not straightforward. Here, we develop an alternative description of such metasurfaces based on coupled-mode theory and provide an explanation for this intriguing effect. Quite surprisingly, our theory shows that broadband anomalous reflection and transmission, does not necessarily require the use of spatial gradients, but they can be achieved through suitably designed periodic arrays of resonant particles. In addition to their theoretical importance, our results can be important for the design of efficient metasurfaces with specified frequency response.

Suppressing the unwanted scattering from an antenna while maintaining its optimal absorption capabilities is desirable in many practical applications. However, traditional techniques to suppress the scattering of a receiving antenna typically come at the price of significantly lowering the absorbed power, and are thus unfavorable for realistic applications. On the contrary, we prove that the proper interference of multiple scattering modes can decouple the constraints on scattering and absorption of a system, opening a new venue to implement an efficient sensor with minimized scattering signature. Here, we theoretically and experimentally present the design of microwave antennas based on overlapped electric and magnetic dipolar modes, observing over 6-dB scattering suppression without sacrificing absorption. The presented technique is of special interest for non-invasive sensing and radar technology.

Here we present the design and numerical results for an ultrathin unidirectional carpet cloak based on the restoration of the phase of the reflected wave. This ultrathin carpet cloak conceals a triangular surface bump with center height of 4.1 mm and tilt angle of 20 deg. The cloaking metasurface consists of an array of closed ring resonators, which allow an efficient phase manipulation along the edge of the bump. The numerical results at operation frequency f0 = 80 GHz demonstrate a good performance of the designed cloak in both near field and far field. The presented cloak has a thin, lightweight, and easy to fabricate design for radio and THz frequencies and can find applications in radar and antenna systems.

In this talk, we review our recent work on the linear and nonlinear operation of optical antennas, bridging far-field radiation with the near-field interactions between light and matter. We discuss the use of plasmonic and dielectric nanoparticles, and combinations of them, to locally enhance linear and nonlinear optical field interactions, to efficiently trap, absorb, scatter the incident light, to receive and transmit nanoscale signals through wave propagation and radiation, and to tailor the impinging radiation at a subwavelength scale. We discuss in particular the relevance of translating established concepts of radio-frequency antenna theory into the realm of nano-optics, and the inherent challenges and unique opportunities associated with this field of science and technology. In our talk, we will provide physical insights into the proposed nanoantenna geometries, and discuss a variety of nanodevices aimed at processing and tailoring in unconventional ways the nanoscale interaction of nanoparticles with light. We will discuss the concepts of meta-transmitarrays and meta-reflectarrays, obtained by suitably patterning metasurfaces in the transverse direction with suitably designed nano-antennas, in order to tailor at will the impinging light. We will also discuss how these concepts may be extended to nonlinear operation and to time-varying systems. Finally, we will discuss the realization of magnetic nano-antennas that can enhance and exploit the typically weak magnetic effects at visible frequencies using proper arrangements of plasmonic nano-clusters, as well as the application of nano-antennas to realize single and multiple wireless links for light, opening exciting possibilities for nanophotonics and broadband optical communications. More generally, we will provide an overview of the exciting possibilities opened by the fields of plasmonics and metamaterials when combined with antenna concepts, and the fertile ground opened by the combination of these fields of research.

Optical metasurfaces, or planarized metamaterials, are based on engineered subwavelength inclusions intentionally designed to provide desired advanced functionalities, unavailable with conventional gratings, by exploiting their anomalous localized response. Metasurfaces have been investigated both theoretically and experimentally in various recent studies, but most of the available examples are limited to strictly periodic structures. In this work we introduce a novel planarized metasurface reflector composed of deeply subwavelength nonperiodic inclusions arranged to impart the desired arbitrary phase distribution at the nanoscale. We obtain exciting and unique wave interaction properties, and we outline their potential applications at optical frequencies, demonstrating a novel photon management approach for broadband light absorption enhancement in thin-film solar cells, an efficient, low-dispersion integrated on-chip coupler, and a new concept for ultrathin optical carpet cloaks.

Summary form only given. Electro-optic (EO) devices are extensively used in various THz applications such as THz Time-Domain Spectroscopy (THz-TDS), THz Imaging, Ranging, and Detection. These devices are commonly designed without rigorous theories since there have been a few full-wave numerical approaches for simulating wave interactions in EO crystals. The objective of this work is to present a time-domain full-wave analysis for this purpose. It has been shown that the Pockels effect in electro-optic crystals leads to nonlinear cross-phase modulation (XPM) induced by the time-dependent electric fields of an intense terahertz pulse [Y. Shen et al., Phys. Rev. Lett. 99, 043901 (2007)]. As a result, a spectral shift is observed in optical pulses propagating through an EO crystal in the presence of an intense THz pulse. In this work, we propose an appropriate implementation of nonlinear finite-difference time-domain method (NL-FDTD) for the modeling of electromagnetic wave interactions in a nonlinear, dispersive, and anisotropic medium. The Lorentz model commonly used for formulation of the dispersion in EO crystals has been adopted in the NL-FDTD analysis as a result of which a complete numerical analysis including the dispersion and anisotropy of nonlinear crystals has been implemented for modeling the performance of EO devices. We have applied our formulation to a typical EO device, namely a THz beam sampler. The structure of the sampler contains a 0.5 mm-thick (110) ZnTe crystal. The intense THz beam to be sampled by an optical probe along with the probe laser pulse are considered as the incident waves to the ZnTe slab. By means of the simulation of the induced XPM in these crystals, we precisely evaluate the wavelength shift of an optical beam in the EO slab. The calculated wavelength shift is then used for obtaining an estimation of the equivalent walk-off parameter in these slabs. This parameter can be used effectively for modeling an EO crystal and thus for modeling the copropagation of THz pulses and laser probe pulses through these structures.

We present ultrathin plasmonic reflectarray metasurfaces for arbitrary shaping of the wave phase front at infrared and optical frequencies. The metasurface building blocks are designed exploiting nanocircuit concepts, offering high controllability and low loss. We present a fast and accurate analytical model to tune the metasurface and achieve large conversion efficiency over a broad angular range and moderately broad bandwidth of operation. We suggest the application of these concepts for light manipulation, trapping and harvesting in solar cells technology.